The degradation of the water quality in our lakes, rivers, and streams has many causes, including agricultural or sewage pollution, over-fertilization of surrounding land areas, fallen foliage, coniferous plantations, and acid rain. In some situations, a eutrophic environment is established and results in formation of sediments, excessive algae and aquatic plant growth, high organic matter content, formation of foul odor-causing substances, and water turbidity. These have harmful effects on fish and other aquatic animals and plants. Turbidity resulting from suspended solids in the water filters sunlight which decreases photosynthesis and thereby reduces the amount of dissolved oxygen available in the water.
Previous attempts to clarify and purify eutrophic waters have often enlisted the use of toxic substances to kill the microorganisms which flourish therein. Other disadvantages, in addition to toxicity, result from this approach. In most cases, the biocidal effect of these toxic substances is incomplete, which allows a rapid recovery by the microorganisms. Thus, the results are only temporary and are generally ineffective.
Examples of such uses of toxic substances include the use of heavy metals and their salts, such as copper sulfate. Copper sulfate is virtually the only chemical agent used to control the planktonic algae that cause the majority of aesthetic and water quality problems. Although the province of Alberta, Canada has prohibited the use of copper on all surface waters, in the United States it is currently permitted in water used for swimming, fishing, irrigation, and consumption by both livestock and humans.
Primary U.S. producers estimate the current annual consumption of copper sulfate for water treatment at 5700 metric tons. Most of the copper used is in the form of a pentahydrate (CuSO.sub.4 .multidot.5H.sub.2 O), which is approximately 25% copper by weight. Formulators buy the material from the primary producers and distribute the pentahydrate in crystals, granules, and powders (snow) under the trade names Blue Copper.TM., Bluestone.TM., and Blue Vitrol.TM..
Scientific studies show copper is toxic, and prolonged use breeds copper resistant strains of algae. Recent public concern over environmental and economic issues are expected to ultimately result in a reduction in the use of copper as an algicide. Municipalities are among the largest users of copper. A single municipality in Minnesota terminated a reservoir treatment program due to environmental pressure, and in so doing reduced the entire state's use of copper surfate for algae control from 145 tons in 1989 to 66 tons in 1990.
Copper salts, especially the widely used copper sulfate, are contact herbicides and do kill most forms of algae. They fail, however, to eliminate the cause of excessive algal growth, i.e., the high nutrient levels associated with eutrophic water conditions. The use of copper salts can cause the algal cells to sink to the lake bottom where they are quickly decomposed by bacteria, thereby releasing nutrients, especially orthophosphates, into the water. These released nutrients can then potentiate a new algal bloom. Thus, the problem of algal blooms is only temporarily and incompletely addressed by the use of copper salts.
Introduction of the toxic substances into surface waters can also kill the desirable aquatic plant and animal life. Even if the quantities of toxic substances are rigidly monitored and controlled, repeated treatments are necessary due to the temporary efficacy, resulting in accumulation of the toxic substances within the system and bioaccumulation in fish and other aquatic organisms. Also, studies have shown that blooms of copper-resistant algae occur following copper treatment.
Attempts have been made to circumvent the use of highly toxic substances. Potable water treatment plants commonly treat water by using poly-aluminum chloride (PAC) as a flocculent to precipitate algae. Problems can occur when the algal concentrations are relatively low because the algae simply do not flocculate and go right through the filters. Also, living algal cells do not flocculate or tend to escape from the floc. Therefore, the algae must first be killed with an ozone treatment and must be in relatively high concentration before flocculation can occur with the use of PAC.
In addition, the flocs formed by treatment with PAC are described as very "fluffy," i.e., having low density, and having extremely high water content. These flocs are very difficult to filter and to dewater.
A number of basic reactants, including calcium hydroxide, calcium oxide, magnesium hydroxide and oxide have been employed with flocculents and are sometimes termed co-flocculents. These basic substances, however, can increase the pH of the treated waters to the level of endangering the aquatic plants and animals. For example, if these basic substances are used in amounts which increase the pH into the dangerous zone above pH 9, undissociated bases, e.g., ammonia, can provoke mass mortalities in fish and other organisms. In addition, these basic reactants are caustic and can present a health hazard for the personnel using them. Application rates for these compounds therefore have to be very precise in order to avoid harmful side-effects. In certain areas, their use is restricted due to their non-natural origin, their health hazards, and their potentially damaging effects on the aquatic environment.
Natural substances such as coccolithic calcium carbonate have been successfully employed for water-related applications in Europe. When sprayed over a pond surface, for example, the product will eventually settle on the organic mud sediments and accelerate their mineralization. However, coccolithic calcium carbonate, when used alone, has proven unsuccessful in subtropical or tropical climates such as Florida, where sunlight and other conditions are more conducive to rapid algal growth.
Therefore, more effective non-toxic compositions and techniques for purification and clarification of water are clearly needed.